Electrical lead-through for pressure intensifier



April 12, 1966 R. P. LEVEY, JR 3,245,120

ELECTRICAL LEAD-THROUGH FOR PRESSURE INTENSIFIER Filed March 19, 1965 IN N VE TOR.

I Ralph P. Levey, Jr. Fig. 1. BY

ATTORNEY.

United States Patent 3,245,120 ELECTRICAL LEAD-THROUGH FOR PRESSURE INTENSIFIER Ralph P. Levey, Jr., Oak Ridge, Tenn., assignor to the United States of America as represented by the United States Atomic Energy Commission Filed Mar. 19, 1965, Ser. No. 441,393 5 Claims. (Cl. 18-16) This invention relates generally to pressure intensifiers and more particularly to an improved electrical leadthrough for the movable piston of a piston-cylinder type high pressure intensifier.

Very high pressures have been utilizedto effect material densification, phase transformations, and chemical changes. In many instances however, attainable pressures are insufficient to produce the desired result. In other cases the necessary pressure can be produced on very small samples only, making commercial application impractical. An additional factor which lessens the desirability of using the high pressure alone, is the very high cost of pressure intensifiers which increases exponentially with. pressure for any given working volume.

In practically all instances where densification or chem.- ical reactions are accomplished through the application of high pressure, a considerably lower pressure would be sutficient if the temperature of the workpiece under pressure were raised. To accomplish such a rise in temperature a resistance type heating element is normally .used. Such a heating arrangement requires electrical power supplying leads which must pass through one of the pistons or the cylinder wall in a piston-cylinder type pressure intensifier. Additional leads are also required such as instrumentation leads to temperature measuring thermocouples.

The passing of electrical leads from the outside of the pressure intensifier to its innermost high pressure cavity Of the leads due to the lesser ability of the leads and their supporting packing to support large pressure-induced loads. When the electrical leads are used to supply resistance heaters within the interior of the pressure intensifier, the magnitude of the problem is increased due to the necessarily large cross sections of the leads. A lesser problem exists where the leads are of the smaller size used for instrumentation. Leads of both types are typically used where heat is applied to the high pressure cavity. The severity of the problem increases as the pressures developed within the intensifier increase.

Prior art schemes for passing electrical leads into pressure intensifiers have been generally limited to conductor cross sections which are less than one tenth of one percent of the loaded cross section. This has been due to the relatively large seal space necessary to pass any given size conductor into a high pressure intensifier. The resulting problem is especially serious where it is desired to pass relatively large power leads into pressure intensifiers of relative small cross section.

It is accordingly, a general object of the invention to provide improved means for admitting electrical leads into the interior of a pressure intensifier.

Another object of the invention is to provide a seal which requires a minimum amount of space for the passing of an electrical conductor therethrough.

Another object of the invention is to provide means for passing electrical leads into the interior of a pressure intensifier wherein the cross section of the leads comprises from one to two percent of the area under load.

Other objects of the invention will become apparent from an examination of the following description of the invention and the appended drawings, wherein:

FIGURE 1 is a vertical sectional view of a piston member incorporating the invention for use in a pistoncylinder type pressure intensifier.

FIGURE 2 is a top plane view of the piston member of FIGURE 1.

FIGURE 3 is an enlarged, horizontal, partial sectional view of the piston member of FIGURE 1 showing the centrally located seal area in greater detail.

FIGURE 4 is an enlarged, vertical, partial sectional view of the piston member of FIGURE 1 showing the passage of electrical leads through the upper radially extending seal area.

In accordance with the present invention, an improved means for admitting electrical leads to the interior of a piston-cylinder type pressure intensifier is provided. A longitudinally tapered opening is provided into the interior of the pressure intensifier. The opening has its smallest area nearest the exterior of the intensifier. Electrical leads are passed through the opening which is then filled with a mixture of epoxy ceramic material. The concentration of the ceramic material within the epoxy is chosen so as to provide a concentration gradient commencing with substantially percent epoxy nearest the pressure chamber of the intensifier and becoming progressively more concentrated with ceramic material until about 50 percent ceramic material and 50 percent epoxy exists at the end of the tapered opening.

To fa-ciliate an understanding of the invention, reference is made to FIGURE 1 of the accompanying drawings wherein a T-shaped piston member 1 of circular horizontal cross-section is illustrated. The enlarged end 2 of piston member 1 is capped by a circular disk member 3 of equal diameter with end 2. The smaller end 4 of piston member 1 is provided with a pair of grooves 5 on its exterior surface for the receipt of O-rings therein. Piston member 1 also contains a centrally located longitudinal bore 6. The uppermost portion of end 2 is provided with a groove 7 which communicates between central bore 6 and the periphery of circular disk member 3. When groove 7 is covered by disk member 3, a passageway of semicircular cross-section is created between bore 6 and the exterior of piston member 1. A cylindrical dowel 12, having an axis parallel to the axis of piston member 1, is fixed at one end to enlarged end 2 of piston member 1. Cylindrical dowel 12 prevents the enlarged end 2 of piston 1 from becoming jammed in a cylindrical die cavity during a pressing operation.

FIGURE 2 shows a top view of the piston member of FIGURE 1. In FIGURE 2 the circular configuration of disk member 3 may be seen together with a suitable arrangement of bolts 13 for securing disk member 3 to piston member 1. Also illustrated in FIGURE 2 as well as in FIGURE 1 is an electrical connector 11 provided at the exterior terminals of electrical conductors -8 and 9 which pass through bore 6 and groove 7.

FIGURES 3 and 4 depict the cross sectional configurationof bore 6 and groove 7 respectively. A suitable grouping of electrical conductors 8 and 9 are illustrated in FIGURES 3 and 4 showing their relative positions within bore opening 6 and groove 7. The space between the conductors is filled with a mixture of ceramic material such as alumina with epoxy.

Refer-ring again to FIGURE 1, after the conductors 8 and 9 are in position within central bore 6 and groove 7, they are potted in place with an alumina-epoxy mixture of increasing alumina content as one progresses from end 4 of piston member 1 through bore 6 to groove 7. The mixture is approximately 50 percent alumina where bore 6 reaches opening 7 and 100 percent epoxy nearest end 4. The extreme end of bore 6 adjacent end 4 of piston member -1 is substantially closed by a urethane pad 10, with the exception of openings for the conductors 8 and 9 to pass therethrough.

Bore 6 is tapered along its length by about 0.1 degree, having its greatest cross-sectional area nearest end 4 of piston member 1 and its smallest cross-sectional area at the junction of bore 6 and groove 7. This taper and the graded concentration of alumina and epoxy along the length of bore 6 combine to provide a seal for conductors 8 and 9. It is noted however, that the concentration gradient in the alumina epoxy mix will provide an improved seal even where no taper is provided.

The use of a right angle in the path followed by the seal also contributes to the ability of the seal to support large pressure diiterentials. This feature is independent of the invention however, and seals constructed according to the present invention could be made to pass straight through the piston.

During a pressing operation, exposure to the high pressure within the intensifier causes the ceramic-epoxy mix (potting. material) surrounding the electrical conductors to become plastic to a varying degree along the length of the seal, with the greatest degree of plasticity beginning at its innermost high pressure. end where the epoxy concentration is greatest. That portion of the mix which be comes plastic exerts a greater pressure against the conductor passing therethrough as well. as the walls of the bore or opening. The magnitude of the pressure exerted by the mix approaches the pressure developed within. the intensifier in the seal portion immediately adjacent. to the pressure chamber of the intensifier. Grading of the ceramic concentration in the mix controls the plasticity gradient of the seal when under pressure. Due to the increased pressure exerted by the. mix against the conductors and against the bore wall, an increased frictional force is available to hold the conductors and potting material within the bore. This increase in frictional force permits about a ten fold increase in the allowable conductor cross section which may be passed through a given size piston.

A suitable epoxy for use in the invention is Shell Epon 828 epoxy with a TETA curing agent. This epoxy can be mixed with alumina of varying proportions up to about 50 percent.

In one embodiment of the preferred embodiment as illustrated in FIGURES 1-4, a bore 6 was provided whose diameter varied from 0.125 in. at end 4 to 0.110 in. at the point of intersection of bore 6 with groove 7. Into bore 6 were placed two number 16 wires and. four number 18 wires. An epoxy-ceramic mix varying from 100 percent epoxy at end 4 to 50 percent epoxy and 50 percent ceramic at groove 7 was then packed around the wires.

As a practical consideration, a smooth continuous gradient in the ceramic concentration of the potting material cannot be achieved. Although such a gradient is most desirable, suitable gradients may be achieved by providing incremental step changes in the concentration of ceramic material. It will be apparent to those skilled in the art that the smallest practical increments should be used.

The above description of the invention was ode-red for illustrative purposes only, and should not be interpreted on a limiting sense. 'It is intended rather that the invention be limited only by the claims appended hereto.

What I claim is:

1. Improved means for passing electrical leads into the high pressure cavity of a piston-cylinder type pressure intensifier comprising: a right cylindrical piston having an axial passageway, said electrical leads passing through said. passageway, and a mixture of epoxy and ceramic material packed into said passageway about said. electrical leads, the concentration of said ceramic material in said mixture increasing with increasing. distance from said. high pressure cavity.

2. The improvement of. claim .1 wherein the concentration ofv said ceramic material in said. mixture varies from 0 to about percent.

3. The improvement of claim. I wherein ceramic. material comprises almuina.

4. Improved means for passingelectrieal leads into the high. pressure cavity of a piston cylinder type pressure intensifier comprising: a right cylindrical piston having a tapered, centrally located, axial passageway of circular cross-section, said passageway having its larger cross-section end nearest said high pressure cavity, said electrical leads passing through said tapered passageway; and a mixture of epoxy and. ceramic material packed into said tapered passageway about said electrical leads, the concentrations of said ceramic material and said epoxy in said mixture varying so :as to provide a concentration gradient commencing with essentially pure epoxy nearest said high pressure cavity and becoming progressively more concentrated with ceramic material until said mixture becomes substantially half ceramic material and half epoxy in said passageway near the exterior of said intensifier.

5. The improvement of claim 4 wherein said ceramic material comprises alumina.

No references cited.

LARAMIEv E. ASKIN, Primary Examiner. 

1. IMPROVED MEANS FOR PASSING ELECTRICAL LEADS INTO THE HIGH PRESSURE CAVITY OF A PISTON-CYLINDER TYPE PRESSURE INTENSIFIER COMPRISING: A RIGHT CYLINDRICAL PISTON HAVING AN AXIAL PASSAGEWAY, SAID ELECTRICAL LEADS PASSING THROUGH SAID PASSAGEWAY, AND A MIXTURE OF EPOXY AND CERAMIC MATERIAL PACKED INTO SAID PASSAGEWAY ABOUT SAID ELECTRICAL LEADS, THE CONCENTRATION OF SAID CERAMIC MATERIAL IN SAID MIXTURE INCREASING WITH INCREASING DISTANCE FROM SAID HIGH PRESSURE CAVITY. 